From the obtained experimental evidence for surface states, we believe the superconducting state of the Bi\(_{2}\) Te\(_{2.7}\) Se\(_{0.3}\)  alloy in Phase I can have nontrivial topology.
When the bulk pairing is \(A_{1g}\)  phase (\(s\) -wave), the bulk is fully gapped, surface states form the Fu-Kane model[1]} in 2D, and Majorana zero modes should be found in the vortex cores on the surfaces.
When the bulk pairing is \(A_{1u}\)  phase, the fully-gapped bulk realizes topological superconductivity in class DIII in 3D[2]}, and the the surface states are recognized as helical Majorana surface states, which should lead to an asymmetric surface tunneling spectroscopy[3]}, [4]}, [5]}.
The bulk pairing symmetry can also be two-component \(E_u\)  phase according to recent data, which can spontaneously break in-plane rotation (time-reversal) symmetry and falls into the nematic (chiral) phase.
In the nematic phase, topological superconductivity in class DIII is realized in 3D, and the surface states are helical Majorana surface states[6]}, [7]}, where the in-plane critical fields should be anisotropic[7]}, [9]}.
While in the chiral phase, bulk superconductivity is nodal with point nodes, and Weyl superconductivity is realized. The surface states are thus Majorana arc states connecting surface-projected Weyl points with opposite Chern numbers[10]}. In the chiral phase, time-reversal breaking signals such as Kerr rotation should be observed.
These results and discussions above are summarized in Table 1.
